Chitosan is the commonly used name for poly-[1-4]-β-D-glucosamine. Chitosan is commercially available and is chemically derived from chitin, which is a poly-[1-4]-β-N-acetyl-D-glucosamine. Chitin is the second most abundant polysaccharide after cellulose and is found widely in nature, for instance in the cell walls of fungi, the exoskeletons of insects and, in particular, the exoskeletons of crustaceans.
Chitosan is produced by deacetylation of chitin. The degree of deacetylation may vary but generally is at least 60%. Commercially available chitosans have a degree of deacetylation of from 60 to 100%, typically of from 75 to 95%.
Within the scope of the present specification the terms “chitosan” and “poly-[1-4]-β-D-glucosamine” may be used interchangeably to denote a poly-[1-4]-β-D-glucosamine having a degree of deacetylation of at least 60%. Totally deacetylated chitosan contains recurring units of formula (I):

According to common practice the carbon atom bearing the amino —NH2 group is indicated as the “C-2 position”, whereas the primary carbon atom of the —CH2OH group in formula (I) as the “C-6 position”. The bond between adjacent recurring units involves the carbon atoms in the C-1 and the C-4 positions as indicated by the notation [1-4]. Depending on the orientation of the —OH group in the C-1 position (axial or equatorial) the glucosamine unit is defined as α-D-glucosamine or β-D-glucosamine. For the sake of simplicity in formula (I) and in the subsequent formulas the units will be drawn as β-D-glucosamine units although the invention encompasses both configurations.
Chitosan is frequently employed as bioactive, biocompatible and biodegradable material in medical and pharmaceutical applications. Additionally, chitosan forms films and fibers provided with high tensile strength. Chitosan films and coatings are also provided with remarkable barrier properties against the permeation of chemical and biological agents while at the same time maintaining permeability to water vapour.
The great current interest in chitosan and some of its derivatives is readily understood.
Only a few fluorine-containing derivatives of chitosan have been previously disclosed.
FR 2640627 (COMMISARIAT A L'ENERGIE ATOMIQUE) 22 Jun. 1990 discloses the reaction of chitosan or polygalactosamine with anhydrous HF to yield oligosaccharides or monosaccharides wherein the —NH2 groups in the C-2 position are in the —NH3(+)F(−) form and the terminal gluco- or galactopyranosyle units have a C—F bond in the C-1 position.
U.S. Pat. No. 6,264,929 (WELLA AKTIENGESELLSHAFT) 24 Jul. 2001 discloses compositions for the treatment of hair which comprise the product obtained by the neutralization of a polymer having basic groups (e.g. chitosan) with a fluorinated acid of formula: A-(CH2)x—(CF2)y—(CH2)z—B wherein x and z may independently be a number from 0 to 5, y is a number from 1 to 21, A is an acid group and B is either a fluorine atom (then z=0) or an acid group.
WO 2008/141452 (RIVAL S.E.C.) 27 Nov. 2008 discloses a process for the preparation of an organosoluble chitosan salt which comprises reacting chitosan with a fluoroalkyl carboxylic acid or a fluoroalkyl sulfonic acid having at least 3 fluorine atoms. Notable examples of suitable acids are trifluoroacetic or trifluoromethanesulfonic acids. The soluble chitosan salts can be used as intermediates for further transformation of the chitosan backbone. Examples are the silylation of the —OH group on the C-6 position using t-butyldiphenylsilyl trifluoroacetate.
US 20030199687 (MANSSUR YALPANI) 23 Oct. 2003 discloses fluorinated biopolymers useful as imaging probes, diagnostic methods and contrast agents. Biopolymers comprising [1-4]-D-glucosamine recurring units are disclosed, however polymers comprising [1-4]-D-glucosamine units having —NH(fluoropolyether) side chains in the C-2 position are not explicitly described. The preparation of said compounds is also not disclosed.
It has now been found that chitosan derivatives containing fluoropolyether chains bound to the nitrogen atom in the C-2 position can be prepared and are provided with unique properties which render them useful in a number of applications.